1. Field of the Invention
The present invention relates to reverse battery protection, current sense, and temperature sense circuits and, more particularly, to a novel circuit for performing all three functions and producing a digital output thereof.
2. Related Art
Conventional power circuits which are connected to a battery (for example and automotive battery) utilize an electromechanical relay and diode combination to protect the power circuit from damage due to reverse battery connections. Current sensing in conventional power circuits is generally accomplished using a shunt resistor.
A conventional power circuit 10, as is used in the automotive industry, is shown in FIG. 1. The power circuit 10 includes a positive DC bus (B+) and a ground terminal for connection to a battery (not shown). Six power transistors, Q1-Q6, form a full bridge circuit for driving, for example, a three phase induction motor. Gate drive control circuits 11, 12, and 13 alternately turn on and off the power transistors Q1-Q6 to produce pulsed power at terminals A, B and C as is known in the art.
A relay circuit, M, is employed to protect the power transistors from damage if the battery is connected in reverse. When the battery is reversed, diode D1 is reverse biased so that current is blocked from flowing through the relay coil. The relay contact then opens to disconnect the battery from the power circuit 10. When, the battery is connected properly, forward current flows through diode D1 and the relay coil such that the relay contact closes and the power circuit is energized by the battery at B.sup.+ to ground.
Current sensing in the conventional power circuit 10 of FIG. 1 is accomplished by sensing the voltage across a shunt resistor R1 as is well known in the art. Temperature sensing in the conventional power circuit 10 is not possible without providing an additional temperature sensing component, for example, a thermocouple, a thermistor or the like.
The conventional power circuit 10 of FIG. 1 is disadvantageous because in the automotive industry information from current sensing and temperature sensing is typically input to a microprocessor or the like in the form of digital information for use by the microprocessor in controlling of the overall operation of the automobile.
Accordingly, there is a need in the art for an inexpensive solution to providing reverse battery protection, current sensing and temperature sensing in a power circuit which employs a minimal number of circuit components and provides a digital interface for delivering the current and temperature information to a micro-processor.